I recently came across a film review of a documentary "Been Rich All My Life" the story of the Silver Belles, five African American women ages 84-96, who performed as dancers at the Cotton Club and the Apollo Theater and still perform on occasion. One of the Belles is Cleo Hayes, former Cotton Club dancer and acquaintance of my mother. She might be able to give you additional information on Duke Ellington. I'm not sure where this documentary is being shown; however, if you 'google' the title or the filmmaker, Heather MacDonald, you may get contact information.
Donna